1. Field of the Invention
The present invention relates to a vibratory roller, especially a trench roller, having four drums that can be vibrated. The drums are driven individually, and are rotatably mounted, in pairs, on a front or rear support means, with the front support means being attached to a front frame, and the rear support means being attached to a rear frame.
2. Description of the Prior Art
Various basic types of steering systems are known for guiding or steering vibratory rollers, namely pivoted bogie steering or fifth-wheel steering, transfer steering, articulated steering, and the so-called panzer steering. With the articulated steering system, the vibratory roller has a front frame and a rear frame that are interconnected via a hinged or swivel coupling. Each frame supports a pair of drums. The front and rear frames are pivotable relative to one another, via a steering cylinder or the like, through a specific angular range, which for the drum includes a straight ahead position and toward both sides thereof an angular range for driving in curves toward one side or the other of the roller. With the panzer steering system, the four similarly paired drums are disposed on a common, rigid roller frame. Of the four individually driven drums, in each case the two left or the two right drums can be oppositely controlled, so that thereupon the drums on the one side of the roller can run in the direction opposite to those drums on the other side of the roller, or only those drums on one side of the roller need to be driven, as a result of which, as with the steering system of a tank, it is possible to rotate the roller on the spot.
All of the aforementioned types of steering systems have drawbacks for a trench roller.
The fifth-wheel, transfer, and articulated steering systems require for each change in direction a relatively large turning radius that is determined by the design involved, and that is disadvantageous in narrow trenches, particularly at the site of branches.
Although with the panzer or tank steering system a rotation on the spot about the center point of the roller is possible, thus meeting the necessary maneuverability for a trench roller, this steering system has two further significant drawbacks. One drawback is that for every change in direction, or even slight correction in the direction, the continuous travel must be interrupted in order to stop the drums on one side or, as is necessary in most cases, to operate the left and right drums in opposite directions. The unavoidable consequence of this is that the already compacted surface of the ground is torn up. The other drawback is that the speed with which the direction can be changed (angular speed about a vertical axis), in addition to being a function of the driving speed, also depends on the one hand upon the coefficient of friction between the drums and the ground, and on the other hand depends upon the ratio of the wheel base of the drums to their width. The less the friction, the poorer is the steering effect. When the ground is soft and the drums have partially sunk in, it is no longer possible to steer the roller. The less the width of the drums at a given wheel base, the poorer is the steering effect.
An object of the present invention is to improve the steering condition of vibratory rollers, and especially of trench rollers, in such a way that changes in direction during normal travel, or slight corrections in the direction, can be undertaken rapidly and without damaging the already compacted surface of the ground. In addition, it should be possible to undertake sharp changes in direction practically on the spot when it is necessary to deviate from normal travel, for example at a branch in the trench.